1. Field of the Invention
The present invention relates to a display comprising an electroluminescence (hereinafter referred to as xe2x80x9cELxe2x80x9d) element disposed on a substrate, and particularly to a sealing structure for an organic EL display device including an organic EL layer.
2. Description of the Related Art
A display device using organic EL comprises a self-emissive element which itself generates light when an electric current is made to flow through the element. Such a display device consumes less power compared to a CRT, and does not have the problem concerning viewing angle as in an LCD. Organic EL display devices are therefore regarded as devices that may replace both CRTs and LCDs. FIG. 1A is a plan view of a conventional organic EL display device, and FIG. 1B shows a cross-sectional view taken along line Axe2x80x94Axe2x80x2 of FIG. 1A. A plurality of selective drive circuits 2 are disposed for respective pixels on a transparent substrate 1. Each selective drive circuit 2 is connected with a pixel electrode 4. An organic EL layer 5 including an organic emissive material, and a counter electrode 6 are disposed covering the pixel electrodes 4. Surrounding the pixel region constituted by the selective drive circuits 2, pixel electrodes 4, organic EL layer 5, and counter electrode 6, display driver circuits 7a, 7b are arranged for controlling the selective drive circuits 2 and applying predetermined voltages to the pixel electrodes 4. The driver circuits 7 are connected to terminals 9 by wiring 8. A cap 10 composed of a metal such as aluminum is arranged covering these structures, and is adhered to the transparent substrate 1 using a seal 51. The space 12 between the cap 10 and the transparent substrate 1 is filled with dry nitrogen gas. A desiccant sheet 13 is disposed on the inner surface of the cap 10.
A selective drive circuit 2 may comprise, for example, a plurality of semiconductor elements including thin film transistors (TFT). A first TFT switches between xe2x80x9conxe2x80x9d (conductive state) and xe2x80x9coffxe2x80x9d (non-conductive state) in response to the output from the driver circuit 7a. When the first TFT of a selective drive circuit 2 is turned on by an output from the driver circuit 7a, the corresponding pixel electrode 4 is applied with a voltage according to an output from the driver circuit 7b via a second TFT. An electric current thereby flows between the pixel electrode 4 and the counter electrode 6. The emissive layer 5 is the portion which emits light when a current is made to flow therein by the pixel electrode 4 and the counter electrode 6. The emissive layer 5 emits light at an intensity according to the amount of current flowing between the pixel electrode 4 and the counter electrode 6. The generated light transmits downward in the cross-sectional view through the transparent substrate 1 to be observed.
More specifically, holes injected from the anode and electrons injected from the cathode recombine within the organic EL layer 5. As a result, organic molecules containing the organic EL layer 5 are excited, generating excitons. Through the process in which these excitons undergo radiation until deactivation, light is emitted from organic EL layer 5. This light radiates outward through the side of the transparent anode via the transparent insulator substrate 1, resulting in light emission.
The TFTs and organic EL layer 5 formed through lamination must be shielded from the external atmosphere. A cap 10 made of a metal such as aluminum is therefore adhered to the periphery of the insulating substrate 1 by a seal 51 composed of a sealing material such as epoxy. This arrangement is provided mainly for preventing deterioration of display quality when, for example, a defect such as a pinhole is present in the counter electrode 6. In such a case, moisture entering from the pinhole may cause oxidation of the counter electrode 6 or a separation between the organic EL layer 5 and the counter electrode 6, producing dark spots and resulting in degradation of display quality. In this light, the cap 10 not only protects the display region and the driver circuits 7 from physical shock, but also serves to prevent moisture from entering the device. The cap 10 is therefore formed in a shape of a tray covering the display region. Further, to prevent damage by penetrating moisture, the space 12 inside the cap 10 is filled with an inert gas such as dry nitrogen or helium, and the desiccant sheet 13 is disposed. A stepped portion may be provided in the location for arranging the desiccant sheet 13. The structure as described above is disclosed, for example, in Japanese Patent Laid-Open Publication No. Hei 9-148066.
However, in a conventional sealing structure, moisture may still be present inside the device. For example, moisture may be present in the nitrogen gas filled in the space 12. Moreover, as the desiccant sheet 13 is arranged on the cap 10, it is possible that moisture may adhere to the organic EL layer without being adsorbed by the desiccant sheet 13.
The object of the present invention is to provide an element sealing structure for reliably preventing penetration of moisture into areas around self-emissive elements without increasing the device thickness.
Another object of the present invention is to enhance the aperture ratio of each pixel while realizing a reliable sealing structure.
A further object of the present invention is to simplify the device manufacturing process while realizing a reliable sealing structure.
The present invention for achieving the above objects provides a display device in which a display region having a self-emissive element is formed between a pair of substrates, wherein a resin having a desiccant mixed therein is disposed between the pair of substrates.
Another aspect of the display device of the present invention is that the pair of substrates are adhered to one another by a sealing material disposed surrounding at least the display region, so as to seal the display region including the self-emissive element.
A further aspect of the display device of the present invention is that the self-emissive element is an electroluminescence element, and especially an organic electroluminescence element.
According to the display device of the present invention as described above, a resin having a desiccant mixed therein is disposed between a pair of substrates. Moisture penetrating inside the display device can be adsorbed by the desiccant, thereby preventing deterioration of the display region by the moisture.
Furthermore, the pair of substrates are adhered to one another by a seal formed surrounding the display region, and a desiccant is mixed in the seal. The amount of moisture permeating through the substrates is negligible. The moisture permeating through the seal is adsorbed by the desiccant. Accordingly, almost no moisture penetrates inside the display device, and deterioration of the display region by moisture can effectively be prevented.
In another aspect of the display device of the present invention, the display region having the self-emissive element is formed on the first substrate among the pair of substrates, the second substrate is arranged facing the display region side of the first substrate and adhered to the first substrate, a color component is provided in the gap between the second substrate and the display region, and the second substrate is a transparent substrate which transmits at least visible light.
As described above, a color component is provided between the display region and the second substrate facing the first substrate having the display region formed thereon. Further, the second substrate is a transparent substrate which transmits visible light. According to this arrangement, the aperture ratio of the display pixels can be enhanced, and increased freedom is available in selecting the size and the driving capability of a TFT when using a TFT for driving the display region. By providing a color component on a separate substrate facing the substrate having the TFT, the manufacturing process can be simplified. Furthermore, the present device prevents display deterioration due to moisture.
In a further aspect of the display device of the present invention, the display region having the self-emissive element is formed on the first substrate among the pair of substrates, the second substrate is arranged facing the display region side of the first substrate and adhered to the first substrate, and a spacer composed of a desiccant is provided in the gap between the second substrate and the display region.
As described above, between the display region and the second substrate facing the first substrate having the display region formed thereon, a fluorescent converting layer which converts a light having a predetermined color into a light of a different color is provided as a color component. Further, a spacer composed of a desiccant is disposed between the fluorescent converting layer and the display region. Accordingly, moisture inside the display device can be adsorbed even when no desiccant sheet is included. In addition, the aperture ratio of the display device can be improved because the spacer is made of a desiccant, and there is no need to dispose a separate desiccant other than the spacer itself.
In a still further aspect, the present invention provides a display device in which a display region having a self-emissive element is formed between a pair of substrates, wherein the pair of substrates are adhered to one another by a sealing material disposed surrounding at least the display region to seal the display region, a groove is formed in at least one of the pair of substrates on a side facing the other substrate in a location where the sealing material is disposed, and a desiccant is filled in the groove.
Another aspect of the display device of the present invention is that a resin having a desiccant mixed therein is used as the sealing material.
As described above, a groove is formed surrounding at least one of the substrates, and desiccant is filled in the groove. Accordingly, desiccant can be disposed at a plentiful amount in the groove, and moisture permeation can be prevented more reliably.
Furthermore, as the groove is covered with the seal for adhering the pair of substrates to one another, the desiccant in the groove is not exposed to the external atmosphere. The desiccant is thereby prevented from adsorbing unnecessary moisture, and can serve for a longer period of time to adsorb moisture permeating through the seal.
In addition, moisture can be adsorbed uniformly from the entire display region because the resin having the desiccant mixed therein is formed covering the display region. According to this arrangement, moisture can be adsorbed more effectively than by disposing a desiccant sheet. Moreover, thickness of the display device can be reduced because there is no need to dispose a desiccant sheet.
Moreover, the resin formed covering the display region fills between the display region and the second substrate facing the first substrate having the display region formed thereon. Unnecessary space is thereby eliminated, further reducing the thickness of the display device while still preventing deterioration by moisture.
According to another aspect of the present invention, there is provided an electroluminescence display device in which an emissive display region having a self-emissive element is formed on a transparent first substrate, wherein the self-emissive element comprises a first electrode, a second electrode, and an emissive element layer formed between the first and the second electrodes. The self-emissive element is covered with a coating resin layer composed of a resin cured by ultraviolet irradiation. Further, a second substrate which transmits ultraviolet rays is arranged over the coating resin layer so as to face the first substrate.
A further aspect of the electroluminescence display device of the present invention is that a desiccant is mixed in the coating resin layer.
A still further aspect of the electroluminescence display device of the present invention is that the coating resin layer having a desiccant mixed therein covers the self-emissive element and fills the gap between the first and the second substrates.
In another aspect of the electroluminescence display device of the present invention, the self-emissive element is composed by laminating, in order from the first substrate side, the first electrode, the emissive element layer, and the second electrode, and the coating resin layer covers the self-emissive element from the second substrate side.
In a further aspect of the electroluminescence display device of the present invention, a light-shielding layer for blocking ultraviolet rays is disposed between the emissive element layer and the coating resin layer.
In a still further aspect of the electroluminescence display device of the present invention, the second electrode simultaneously serves as the light-shielding layer.
According to the above-described arrangement, ultraviolet light can be irradiated through the second substrate to cure the coating resin layer. At that time, the light-shielding layer prevents irradiation of ultraviolet rays on the organic EL layer and on the selective drive circuits formed within the display region on the active matrix panel, which in turn prevents transformation and deterioration of the selective drive circuits and the organic EL layer.
When the second electrode simultaneously serves as the light-shielding layer, the selective drive circuits and the organic EL layer can be protected from ultraviolet irradiation by the second electrode without providing a separate light-shielding layer, while the second electrode sufficiently operates as an electrode. By using a metal second electrode, ultraviolet light can be reflected. The reflected ultraviolet light can again be irradiated on the coating resin layer, increasing the efficiency of ultraviolet irradiation.
Further, moisture is prevented from adhering to the organic EL layer because a desiccant is mixed in the coating resin layer. Accordingly, deterioration due to moisture can be prevented, achieving a display device having a long life. Thickness of the display device can be reduced because there is no need to dispose a desiccant sheet. Moreover, water resistance is further enhanced compared to when a desiccant sheet is used, because the coating resin layer including a desiccant uniformly covers the display region.
The desiccant is a substance having a chemically adsorptive property in the form of a powder having a particle diameter of 20 xcexcm or smaller. The desiccant is mixed in the resin sealing layer by at least 10 wt %, but no more than 50 wt %. In this way, sufficient moisture absorption can be achieved without obstructing hardening of the resin having the desiccant mixed therein, and without reducing the resin viscosity before curing or the resin hardness after curing.